It is conventional to use spring biased contact assemblies, or probes, in testing printed circuit boards and other electrical apparatus for electrical continuity and the like. Typically, contact probes, generally comprising a center signal contact and an outer shield or ground contact, are mounted in a support and brought into relative movement with a device to be tested, such as a circuit board. Upon engagement with the test sites relative movement is continued for a selected distance, e.g., 0.090 inch is conventionally used in the industry, to ensure optimum contact engagement. Tests are performed by sending electrical signals through the test sites to check for electrical continuity and the like.
In carrying out such testing it is important that the contact assemblies have electrical characteristics closely matching the electrical characteristics of the electrical cable with which the contact assemblies are used. Further, signal mistiming, delay and degradation need to be minimized in using such contact assemblies. This is especially true when the contact assemblies are used with high speed apparatus where a delay in digital signal propagation can result in false readings.
Contact assemblies have moving parts and inherently have a degree of mismatch within the manufacturing tolerances and materials employed. Any mismatches which do occur are directly related to the length of the contact assemblies so that the longer the assembly, the greater the mismatch.